The antioxidant activity of casein and Maillard reaction products obtained by reaction of casein with glucose or lactose was studied. Antioxidant activity was evaluated in a model system containing methyl linoleate with haemoglobin as a pro-oxidant. Casein was antioxidative and heating casein in the presence of glucose or lactose resulted in enhancement of antioxidant activity. The development of antioxidant activity in reacted casein-sugar mixtures was determined as a function of initial casein and sugar concentration. The observed antioxidant activity of reacted casein-sugar mixtures was due to casein itself and Maillard reaction products resulting from reacting casein with sugar.